读取和发生串口数据

C# code

  private void btnWrite_Click(object sender, EventArgs e)           {                    this.serialPort1.PortName = "COM4";                            this.serialPort1.BaudRate = 9600;                            this.serialPort1.DataBits = 8;                            this.serialPort1.Parity = System.IO.Ports.Parity.None;          this.serialPort1.StopBits = System.IO.Ports.StopBits.One;              if (this.serialPort1.IsOpen == false)                     {                         this.serialPort1.Open();                           byte[] data = Encoding.Unicode.GetBytes(textBox3.Text);            string str = Convert.ToBase64String(data);                serialPort1.WriteLine(str);                   MessageBox.Show("数据发送成功！","系统提示");       ｝  ｝  private void button2_Click(object sender, EventArgs e)           {         第一种接收                byte[] data = Convert.FromBase64String(serialPort1.ReadLine());                     textBox2.Text = Encoding.Unicode.GetString(data);                  serialPort1.Close();                    MessageBox.Show("数据接收成功！","系统提示");                   第二种接收                 int n = this.serialPort1.BytesToRead;                        byte[] buf = new byte[n];                      this.serialPort1.Read(buf, 0, n);                  string receiveData = Encoding.ASCII.GetString(buf);                   MessageBox.Show(receiveData.ToString());      }

为什么第二种接收没有数据？ 第一种接收会卡在 byte[] data = Convert.FromBase64String(serialPort1.ReadLine()); 这一步？ 求指教

[解决办法]
两种迹象表明缓冲区内无数据
你在serialPort1.WriteLine(str); 后马上读取，看看能不能读到数据